Re: [PATCH] linux-user: Fix clang warning for nios2-linux-user code

[Warner Losh]

> On Jan 10, 2022, at 12:17 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> 
> The clang in Ubuntu 18.04 (10.0.0-4ubuntu1) produces a warning
> on the code added in commit f5ef0e518d03 where we use a
> shifted expression in a boolean context:
> 
> ../../linux-user/elfload.c:2423:16: error: converting the result of '<<' to a 
> boolean always evaluates to true [-Werror,-Wtautological-constant-compare]
>    } else if (LO_COMMPAGE) {
>               ^
> ../../linux-user/elfload.c:1102:22: note: expanded from macro 'LO_COMMPAGE'
> #define LO_COMMPAGE  TARGET_PAGE_SIZE
>                     ^
> /mnt/nvmedisk/linaro/qemu-from-laptop/qemu/include/exec/cpu-all.h:231:31: 
> note: expanded from macro 'TARGET_PAGE_SIZE'
> #define TARGET_PAGE_SIZE   (1 << TARGET_PAGE_BITS)
>                              ^
> 1 error generated.
> 
> The warning is bogus because whether LO_COMMPAGE is zero or not
> depends on compile-time ifdefs; shut the compiler up by adding
> an explicit comparison to zero.
> 
> Fixes: f5ef0e518d0331 ("linux-user/nios2: Map a real kuser page")
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I'm probably going to apply this directly once it's reviewed, because
> it fixes a build-break on one of my machines.
> 
> linux-user/elfload.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Warner Losh <imp@bsdimp.com>


> diff --git a/linux-user/elfload.c b/linux-user/elfload.c
> index 329b2375ef1..2993b01e60c 100644
> --- a/linux-user/elfload.c
> +++ b/linux-user/elfload.c
> @@ -2420,7 +2420,7 @@ static void pgb_static(const char *image_name, 
> abi_ulong orig_loaddr,
>         } else {
>             offset = -(HI_COMMPAGE & -align);
>         }
> -    } else if (LO_COMMPAGE) {
> +    } else if (LO_COMMPAGE == 0) {
>         loaddr = MIN(loaddr, LO_COMMPAGE & -align);
>     }
> 
> -- 
> 2.25.1
> 
>